I would have thought all ring and pinions would be heat treated to a certain spec, but they actually went a step further with the COPO's, now that is getting what you paid for. Those cars must be awesome from top to bottom. Thanks for letting me know, the codes puzzled me for a little while. Ron

Nope; a BE axle has a different posi unit in addition to the HD ring & pinion.

Does the BE axle include the HD posi unit that was used in the 'Service Duty' disk brake differentials? That one had more plates, and higher spring pressures than the standard 12 bold posi unit. I didn't know there was a third one, OR that the HD unit was put into passenger car rears. IS the BE unit the only one having such a Posi unit? If you or anyone have more information on the whys/wherefores of this differential, I think it would be very interesting reading for us all.

I had to hunt down my 'Fact Book' to check out the BE info from McNeish. I'd read that before, but quickly since it doesn't relate to my car. It seems that the predominant difference in the BE posi unit was the larger (and fewer) teeth in the spider/axle gear set, with the same posi clutches, but with different posi springs with slightly higher spring pressure (75 vs 50 psi). I suspect that in turns, the BE rear makes a bit more noise in the rear than the standard rear, due to the fewer number of spider teeth, has that been noted previously? In reading that section again, I noted a small error in Jerry's book, when he says the change in the differential housing from the .3894860NF to the 3989341NF pn occurred in September'69. The differential in my mid Sept '69 Z28 has the 341 housing assembly dated '0829', so that change occurred earlier than stated.

Is the BE (4.10 gear set) the only such COPO differential? The differential section in Jerry's book also states there were higher numbered gear sets (4.56 nd .488) available in 1969 via COPO/9511, but the implication is that these rears had the standard Posi setup, since the BE was the only one singled out for the larger spider/axle gear differences??

Note: I just checked my Hooper book *69 Camaro Reference Book*, and on page 362 he lists the DT rear (4.56) with a similar note (with heat treared ring and pinion and spider gears), but notes the DT as being for COPO 9560/9561 HD, and the BE for COPO ZL-1 HD. Is all of this information accurate?

For '69 4.10 was the lowest RPO ratio. A very few cars have factory documents showing COPO 9511 with 4.56 & 4.88 ratios. The 4.88 was in a Z/28, the 4.56s are in L72 COPOs. The axle code for the L72s remains BE. DT was not an axle code; it is the ECL for that particular ratio. COPO Chevelles may have also used the same posi unit; don't know.

In reading that section again, I noted a small error in Jerry's book, when he says the change in the differential housing from the .3894860NF to the 3989341NF pn occurred in September'69. The differential in my mid Sept '69 Z28 has the 341 housing assembly dated '0829', so that change occurred earlier than stated.

We continue to investigate and add data points for the change-over time from when the 860 housing ended and the 341 housing started. There appears to be at least a small overlap.